Supporting Information A2/B3 monomer set Microwave ...

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Supporting Information

Microwave-assisted synthesis of fluorescent carbon quantum dots from

A2/B3 monomer set

Ari Chae,a Yujin Choi,a Seongho Jo,a Nur’aeni,a Peerasak Paoprasert,d* Sung-Young Parka,c*

and Insik Ina,b*

a Department of IT Convergence (Brain Korea PLUS 21), Korea National University of

Transportation, Chungju 380-702, South Korea.

b Department of Polymer Science and Engineering, Korea National University of

Transportation, Chungju 380-702, South Korea.

c Department of Chemical and Biological Engineering, Korea National University of

Transportation, Chungju 380-702, South Korea.

d Department of Chemistry, Faculty of Science and Technology, Thammasat University,

Pathumthani 12121, Thailand.

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2017

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1. Experimental Section

Materials and Characterization

Both SA (ACS reagent, ≥99.0%) and TAEA (96%) were purchased from Sigma-Aldrich Corp.

A household microwave oven (700 W) (Daewoo Electronics, South Korea) was used

throughout the experiments. Dialysis was carried out by using a molecular weight cut-off

(MWCO) membrane (3,500 Da) of Spectrum Laboratories, Inc.

UV-Vis spectra were measured by an Optizen Alpha UV-Vis Smart spectrometer of

(Mecasys, South Korea). The photoluminescence spectra of the CQD solutions were examined

by using a FS-2 Fluorescence Spectrometer (Scinco Corp., South Korea) with a xenon lamp

excitation source (150 W). HRTEM images were taken on a TECNAI F20 system (Philips) at

an operating voltage of 200 kV. AFM images were acquired by a Multimode-N3-AM

nanoscope three-dimensional (3D) scanning probe microscopy (SPM) system (Bruker Corp.).

FT-IR spectra were acquired on a Nicolet iS10 FT-IR spectrometer (Thermo Scientific).

Raman spectroscopy measurements were performed on an ARAMIS Raman spectrometer

(Horiba Jobin Yvon, France) by using 514.5 or 785 nm laser radiation. XRD measurements of

the powder samples were recorded on a D8-Advance X-ray powder diffractometer (Bruker)

using Cu Kα radiation (λ = 1.5406 Å). The XPS spectra were recorded with a Scientific Sigma

Probe spectrometer (Thermo VG). Fluorescence microscopy images of CQD-labelled cells

were obtained using LSM 510 confocal laser scanning microscope (ZEISS).

For the microwave-assisted synthesis of CQDs from SA and TAEA, 3 g (1 eqv.) of SA and

5.572 g (1.5 eqv.) of TAEA were completely dissolved in 10 mL of deionized water in a 250

mL flat-bottomed flask. After loosely wrapping the flask with polyethylene wrapping film, the

mixture solution was treated inside a microwave oven for 5 min (CAUTION! Carry out the

whole experiment inside a fume hood because of the emission of organic volatiles during

the microwave treatment). After the microwave treatment and complete cooling, dark-brown

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solids were obtained, indicating the formation of CQDs. Extraction of the CQDs was carried

out by adding 100 mL of deionized water to the solids and subsequent ultrasonication in a bath

sonicator (500 W) for 30 min. Centrifuging at 4000 rpm for 30 min was carried out to remove

any insoluble precipitates or agglomerates from the CQD solution. Finally, 1.48 g of brown

CQD2 powders was obtained after freeze-drying of the CQD solution obtained after dialysis

using 3,500 Da MWCO membranes for 3 days.

Cell Viability Test and Bioimaging

The cell viability of the CQDs was measured using the MTT assay method. 200 L of MDA-

MB-231 or MDCK cells at a density of 1 × 105 cells/mL was placed in each well of a 96-well

plate. Afterwards, the cells were incubated for 24 h at 37 °C in a humidified 5% CO2

atmosphere. To determine the cellular viability, a stock solution of CQD2 was dissolved in

RPMI medium at a concentration of 1 mg/mL and the stock solution was diluted up to 0.001

mg/mL. The media was removed and the cells were treated with different concentrations of

the CQD2solution. Then, the cells were incubated for another 24 hrs. The media containing

CQD2 were replaced with 180 mL of fresh medium and 20 L of a stock solution containing

15 mg of MTT in 3 mL of PBS and incubated for another 4 h. Finally, the medium was

removed and a 200 L solution of an MTT solubilizing agent was added to the cells and

accurate shaking was performed for 15 min. The optical absorbance was measured at a

wavelength of 570 nm using a microplate reader (Varioskan Flash, Thermo Electron

Corporation). The relative cell viability was measured by comparing the samples with the 96-

well control plate containing only cells. After cell viability measurements, confocal images

were obtained to confirm the stained cells by using a laser scan microscope (CLSM) at 10×

magnification) with excitation wavelengths of 405, 488, and 543 nm.

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2. Supporting Table and Figures

Table S1. Summary of the mass synthesis of lysine-based CQDs through microwave

pyrolysis

Starting Materials Microwavetime (min/W)

Mass Yielda

(wt.-%)PLQYb

(%) Ref.

SA : TAEA(3:1) 20.6 0.7 CQD5

In this workSA : TAEA

(3:2) 45.0 1.3 CQD4In this work

SA : TAEA(1:1) 3.57 24.0 CQD1

In this workSA : TAEA

(1:1.5) 17.3 49.9 CQD2In this work

SA : TAEA(1:2) 3.13 43.5 CQD3

In this workSA : TAEA

(1:2.5) negligible not measured This work

SA : TAEA(1:3) negligible not measured This work

SA : TAEA(1:3.5)

5/700

negligible not measured This work

Citric acid : Urea(1:3.2) 45/750 not reported 14

Ref 36Angew. Chem. Int. Ed. 2012, 51, 12215

Glucose 111/280700 not reported 711Ref 45

ACS Nano 2012, 6, 5102

Glucose : PEG 1500(2g : 4 g) 10/700 not reported not reported

Ref 46Nanoscale 2013, 5,

2655Carbohydrate

(glucose etc. + inorganic ion)

14/750 not reported 3.29.5Ref 47

J. Mater. Chem. 2011, 21, 2445

a Mass yield = (mass of purified CQD / mass of lysine )100%

b PLQY of CQDs (0.1 mg/mL) measured from the relative PL emission compared with that of quinine sulfate (0.1 mg/mL in 0.1 M H2SO4)

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0 20 40 60 80 100

100

1000

10000

Fluo

rese

nce

Inte

nsity

Decay time (ns)

CQD1 CQD2 CQD3

Relaxation time (ns)

Percent (%)

1 0.705 52.3

2 3.30 36.1

3 10.1 11.6

avg 2.73

Fig. S1. Fluorescence decay profiles of prepared CQDs (the emission at 470 nm with the

excitation of 375 nm light).

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200 180 16075 60 45 30 15 0ppm

CQD3

CQD2

HOOH

O

O

NH2N NH2

NH2

TAEA

SA

bc

c b

c

d

d c

Fig. S2. 13C-NMR spectra of profiles of SA, TAEA, CQD2, and CQD3 in D2O.

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4.0 3.5 3.0 2.5 2.0 1.5ppm

HOOH

O

O

SA

a

NH2N NH2

NH2 TAEA

b

c

a

c b

CQD1

CQD2

Fig. S3. 1H-NMR spectra of profiles of SA, TAEA, CQD1, and CQD2 in D2O.

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2.00E+03

3.00E+03

4.00E+03

5.00E+03

6.00E+03

7.00E+03

8.00E+03

9.00E+03

1.00E+04

1.10E+04

1.20E+04

525526527528529530531532533534535536537538539540541542543544545

Cou

nts

/ s

Binding Energy (eV)

O1s Scan10 Scans, 1 m 40.5 s, 400µm, CAE 50.0, 0.10 eV

Created by : C:\xps\S150602A\S150602B\S150602B.VGXOriginal file : S150602B\MXR1 Gun - 400um\1-3\Group\O1s Scan.VGD

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

392393394395396397398399400401402403404405406407408409410

Cou

nts

/ s

Binding Energy (eV)

N1s Scan20 Scans, 3 m 0.9 s, 400µm, CAE 50.0, 0.10 eV

Created by : C:\xps\S150602A\S150602B\S150602B.VGXOriginal file : S150602B\MXR1 Gun - 400um\1-3\Group\N1s Scan.VGD

N1s

O1s

b)

a)

Fig. S4. XPS high resolution O1s and N1s binding peaks of CQD2.

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-20 0 20 40

Inte

nsity

(a.u

.)

Zeta Potential (mV)

-20 0 20 40

Inte

nsity

(a.u

.)

Zeta Potential (mV)

b)

a)

+26.2 mV

+8.7 mV

Fig. S5. Zeta-potential profile of the aqueous solution (0.1 mg/mL) of lysine-based CQD

prepared from microwave pyrolysis for 4 min.

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b)

a)Water Methanol Ethanol

Water Methanol Ethanol

Fig. S6. Photo images of CQD2 solutions (0.1 mg/mL) in water, methanol, and ethanol under

a) day light and b) dark with the 365 nm UV irradiation.

0.21 nm

0.36 nm

Fig. S7. HRTEM image of CQD2 (left) and Fourier transform image of selected area. d-

spacing of 0.36 nm (red circles) is much clearer compared with weaker d-spacing of 0.21 nm

(blue circles).

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0 10 20 30 40 50 60 70 80

Inte

nsity

(a.u

.)

2

11.8o

20.3o

Fig. S8. XRD spectrum of CQD2.

4000 3000 2000 1000 0

Inte

nsity

(a.u

.)

Raman shift (cm-1)4000 3000 2000 1000 0

Inte

nsity

(a.u

.)

Raman shift (cm-1)

b)a)

Fig. S9. Raman spectra of CQD2 on Si wafer with the excitation of a) 514 nm laser and b)

785 nm laser (the sharp peak in the right spectrum is Raman peak of underlying Si wafer.

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Fig. S10. LDH cell viability tests of CQDs with different CQD concentrations.

Fig. S11. Blue fluorescence images (from left to right : PL, bright, and merged cell images)

of MDAMB (above) and MDCK (bottom) cells after incubation with CQD2 (excitation

wavelength of 405 nm).